The Sagittarius dwarf galaxy as a microlensing target

Cseresnjes, P.; Alard, C.

doi:10.1051/0004-6361:20010177

Cited by 23 publications

(38 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…First, the microlensing rate for Sgr sources behind our fields is a factor of $6 larger than for bulge source stars (Cseresnjes & Alard 2001), and the fraction of Sgr events with detectable microlensing parallax signals is a factor of 3 larger for sources in Sgr than for bulge sources. Thus, it would appear that the probability of detecting a microlensing parallax event for an Sgr source is a factor of $20 higher than for a bulge source (assuming that the sources are bright enough for reasonably accurate photometry).…”

Section: Microlensing Parallax Selection Effectsmentioning

confidence: 88%

“…However, for black holes, the evidence indicates that significant kick velocities are rare (Nelemans, Tauris, & van den Heuvel 1999). As an example of such an analysis, let us suppose that the disk and bulge velocity dispersions were negligible relative to the 24 A previous estimate of lensing rates for Sgr source stars has been made by Cseresnjes & Alard (2001), who find a smaller ratio of Sgr/bulge source lensing events than our estimate. This is because they do not consider only microlensing parallax events and because they count the much more numerous events with bulge main-sequence source stars.…”

Section: Likelihood Distance and Mass Estimatesmentioning

confidence: 92%

See 1 more Smart Citation

Gravitational Microlensing Events Due to Stellar‐Mass Black Holes

Bennett

Becker

Quinn

et al. 2002

ApJ

136

134

View full text Add to dashboard Cite

We present an analysis of the longest timescale microlensing events discovered by the MACHO Collaboration during a 7 year survey of the Galactic bulge. We find six events that exhibit very strong microlensing parallax signals due, in part, to accurate photometric data from the GMAN and MPS collaborations. The microlensing parallax fit parameters are used in a likelihood analysis, which is able to estimate the distances and masses of the lens objects based on a standard model of the Galactic velocity distribution. This analysis indicates that the most likely masses of five of the six lenses are greater than 1 M , which suggests that a substantial fraction of the Galactic lenses may be massive stellar remnants. This could explain the observed excess of long-timescale microlensing events. The lenses for events MACHO-96-BLG-5 and MACHO-98-BLG-6 are the most massive, with mass estimates of M=M ¼ 6 þ10 À3 and M=M ¼ 6 þ7 À3 , respectively. The observed upper limits on the absolute brightness of main-sequence stars for these lenses are less than 1 L , so both lenses are black hole candidates. The black hole interpretation is also favored by a likelihood analysis with a Bayesian prior using a conventional model for the lens mass function. We consider the possibility that the source stars for some of these six events may lie in the foreground Galactic disk or in the Sagittarius (Sgr) dwarf galaxy behind the bulge, but we find that bulge sources are likely to dominate our microlensing parallax event sample. Future Hubble Space Telescope observations of these events can either confirm the black hole lens hypothesis or detect the lens stars and provide a direct measurement of their masses. Future observations of similar events by the Space Interferometry Mission or the Keck or VLT interferometers, as explained by Delplancke, Gó rski, & Richichi, will allow direct measurements of the lens masses for stellar remnant lenses as well.

show abstract

Section: Microlensing Parallax Selection Effectsmentioning

confidence: 88%

Section: Likelihood Distance and Mass Estimatesmentioning

confidence: 92%

Gravitational Microlensing Events Due to Stellar‐Mass Black Holes

Bennett

Becker

Quinn

et al. 2002

ApJ

136

134

View full text Add to dashboard Cite

show abstract

“…The mean stellar density and the central coordinates for each area are shown in the panels. Area #1 contains not only MW stars, but also the core of the Sagittarius dwarf galaxy, in a small proportion of ∼1 : 1000 stars, according with Cseresnjes et al (2000).…”

Section: Slicing the Vvv Bulge Cmdmentioning

confidence: 99%

Milky Way demographics with the VVV survey

Saito

Minniti

Dias

et al. 2012

A&A

231

325

View full text Add to dashboard Cite

Context. The Milky Way (MW) bulge is a fundamental Galactic component for understanding the formation and evolution of galaxies, in particular our own. The ESO Public Survey VISTA Variables in the Vía Láctea is a deep near-IR survey mapping the Galactic bulge and southern plane. Particularly for the bulge area, VVV is covering ∼315 deg 2 . Data taken during 2010 and 2011 covered the entire bulge area in the JHK s bands. Aims. We used VVV data for the whole bulge area as a single and homogeneous data set to build for the first time a single colour−magnitude diagram (CMD) for the entire Galactic bulge. Methods. Photometric data in the JHK s bands were combined to produce a single and huge data set containing 173 150 467 sources in the three bands, for the ∼315 deg 2 covered by VVV in the bulge. Selecting only the data points flagged as stellar, the total number of sources is 84 095 284. Results. We built the largest colour-magnitude diagrams published up to date, containing 173.1+ million sources for all data points, and more than 84.0 million sources accounting for the stellar sources only. The CMD has a complex shape, mostly owing to the complexity of the stellar population and the effects of extinction and reddening towards the Galactic centre. The red clump (RC) giants are seen double in magnitude at b ∼ −8• −10 • , while in the inner part (b ∼ −3 • ) they appear to be spreading in colour, or even splitting into a secondary peak. Stellar population models show the predominance of main-sequence and giant stars. The analysis of the outermost bulge area reveals a well-defined sequence of late K and M dwarfs, seen at (J − K s ) ∼ 0.7−0.9 mag and K s 14 mag. Conclusions. The interpretation of the CMD yields important information about the MW bulge, showing the fingerprint of its structure and content. We report a well-defined red dwarf sequence in the outermost bulge, which is important for the planetary transit searches of VVV. The double RC in magnitude seen in the outer bulge is the signature of the X-shaped MW bulge, while the spreading of the RC in colour, and even its splitting into a secondary peak, are caused by reddening effects. The region around the Galactic centre is harder to interpret because it is strongly affected by reddening and extinction.

show abstract

“…Sagittarius events are very important because their identification would mean a change in the determination for the bulge optical depth τ (Cserenjes & Alard 2001) and therefore the angle assumed for the bar inside the galactic bulge. Sagittarius events with detectable parallax have 20 times greater probability of being observed (Bennett et al 2002) detectable parallax.…”

Section: Description Of Derived Light Curvesmentioning

confidence: 99%

Spectroscopic and light curve characterization of bulge microlensing events

Soto

Minniti

Rejkuba

2007

A&A

View full text Add to dashboard Cite

Aims. Microlensing events have been observed regularly by surveys such as MACHO, OGLE and MOA. They offer an excellent way to probe the galactic structure, kinematics and stellar content. We have undertaken a follow-up study of 16 galactic microlensing events to determine masses and locations of the sources of these events within the Galaxy. Methods. Spectroscopy allows us to obtain information about the sources of the events. Low resolution spectra obtained with the Magellan I and II telescopes were analyzed to obtain radial velocities, spectral type and extinction by the method of Kane & Sahu. We also present results for the lens of the event using the microlensing light curve when possible. Light curves have been analyzed with the standard and the parallax models. Results. We have inferred a configuration inside our galaxy for each event, and therefore a lens mass estimation using a suitable galaxy model. Lens mass determination in some cases shows massive lenses that can be considered black hole candidates. This is the case for the events MACHO-98-BLG-6, and OGLE-00-BUL-43. In our sample only three events do not have enough parallax signal for a successful estimation of the lens mass.

show abstract

The Sagittarius dwarf galaxy as a microlensing target

Cited by 23 publications

References 34 publications

Gravitational Microlensing Events Due to Stellar‐Mass Black Holes

Gravitational Microlensing Events Due to Stellar‐Mass Black Holes

Milky Way demographics with the VVV survey

Spectroscopic and light curve characterization of bulge microlensing events

Contact Info

Product

Resources

About